Kept in a group setting with unfamiliar fellow felines, a cat experiences moderately higher stress than when housed alone in a large unit or in the company of kitties with whom he’s already rubbed whiskers, according to the results of a study published in the May edition of the British journal Animal Welfare.

Increased stress among communally housed cats probably results from unnatural situations that wouldn’t normally occur in the wild, surmised the study’s authors, D.S. Ottway and D.M. Hawkins of Anglia Polytechnic University in Cambridge. Related female cats have been known to form social bonds in colonies and even care for one another’s kittens, while male cats are often territorial and solitary. Naturally formed colonies are fairly stable, with cats forming long-term bonds and sticking together around food sources or places of refuge.

“It is proposed here that the evolved social structure of free-ranging cats indicates that natural selection has favoured individuals, either male or female, which confront and display agonistic behaviour towards ‘outsiders’ who are non-relatives and therefore competitors,” wrote the researchers. “Housing large numbers of unrelated adult cats together in groups that frequently experience the addition of newcomers is, therefore, inappropriate and might be expected to adversely affect welfare.”

Unlike their counterparts in the wild, cats in shelter colony housing are trapped in time and space; they can’t flee the scene or force other cats to do so, yet their situation is temporary, often imposing upon them the prospect of more cats coming and going with the regularity of vacationing hotel guests. While some shelters try to reduce stress by avoiding the addition of any new cats to a colony room until all the cats in an original group have been adopted, others, like the one observed by Ottway and Hawkins, add new cats to the mix in a revolving-door fashion.

“The instability of the cats housed communally in this study was likely to be the factor negatively influencing stress levels,” wrote the researchers, “And further study is needed to determine whether, given this level of instability, a lower critical group density can be determined.”

While previous studies have shown that group density correlates highly with stress levels, Ottway and Hawkins surmised that the problems go further than mere numbers, deriving from the “inappropriate and unstable social grouping” that is somewhat inherent to (and inevitable in) shelter colony housing setups. As noted in “Room to Roam” in the March-April 2003 issue of Animal Sheltering, some organizations try to alleviate the instability of the colony environment by separating cats according to “life-stage groupings” that factor in age, gender, health, and sterilization status. But such systems rely on keeping colony numbers to a minimum; keeping too many cats in one room presents difficulties in both matching and monitoring.

Old research shows that “the upper limit on domestic cat group size in naturalistic environments is around ten individuals,” Ottway and Hawkins note. But in the communal setting they examined, a 279-square-meter room contained 65 cats; a 189-square-meter room contained 47 cats, and a 139.5-square-meter room contained 33 cats. (Interestingly, after the conclusion of the study, the shelter greatly reduced the size of its cat colonies.) In the shelter that favored housing cats alone or in pairs, feline residents stayed in 4.5-square-meter single units—the size of some colony rooms in the United States.

Both shelters provided hiding spaces and perches; the shelter with discrete-unit housing placed litter boxes in each enclosure, while the shelter with colony housing set up large gravel areas as “communal toilets.” Researchers did not note this as a potential design problem, but many shelter directors overseeing colony setups emphasize the importance of providing a litter box for each colony resident—since some cats refuse to share litter boxes in any situation. The suggestion appears to be warranted; shelter staff who worked in the colony setting observed by Ottway and Hawkins reported that the “huts” intended for hiding and resting were sometimes soiled with urine and feces.

Even so, no significant differences were found in toilet-use patterns among the colony residents and the single-unit inhabitants; differences in eating, drinking, grooming, and stereotypic pacing behavior were also statistically insignificant.

In assessing stress levels, the researchers used an evaluation method that treats these “subtle physical indicators” as important measurements. While heart rates and levels of corticosteroid hormone secretion are often used as stress barometers, as Ottway and Hawkins point out, the very process of collecting samples like these is likely to create more stress in cats and thus confound the results.

Instead, the “Cat Stress Score” system, derived from a chart developed by the UK Cat Behaviour Working Group, relies heavily on available research of cat behavior in naturalistic settings as the basis for comparison to cat behavior in the shelter. Observing the activities of cats over 15 consecutive weekdays, Ottway and Hawkins noted not just eating and elimination habits but also patterns of sleeping, resting, playing, exploring, prowling, and attempted escaping.

The incidence of “agonistic” behavior resulting from social conflict was low in both the colony and individual-unit settings. In general, though, cats housed with a large group of other cats previously unknown to them were less likely to sleep and rest in close bodily contact with one another and more likely to spend time hiding—behaviors that previous studies have correlated with increased stress levels. Playing, an indicator of good physical health and mental well-being, was nonexistent in the colony setting and observed only incrementally in single units. But its absence may or may not be important, since, as the authors noted, the incidence of playing among adult cats is fairly low in general.

“Only moderate levels of stress were experienced by cats in communal housing,” Ottway and Hawkins wrote. “It is unlikely, therefore, that a long-term reduction in fitness would result. ... The welfare of the communally housed cats was ... poorer, but it appears that the stress experienced was neither extreme nor prolonged.”

Although all the cats in the study had been shelter residents for at least a month, the results would not necessarily apply to longer-term situations, the researchers note. A study of cats staying in colony housing and discrete units for more extended periods might yield the opposite results, they suggested. “This would determine, first, whether further habituation to the physical environment and to group living per se can reduce the stress effects of group instability,” they wrote, “and, second, whether the level of stress experienced by cats housed in discrete units increases with increasing shelter-residence time.”

The size of the single or “discrete” units is also likely to affect the results of a comparison study; the single units observed in this British study were more akin to the size of real-life rooms in the States.

“Discrete-unit housing is not without welfare problems ... and the cost of providing environmentally enriched single units may be prohibitive for the organisations involved,” Ottway and Hawkins added. “Welfare could be improved among cats housed communally if shelters adopted a policy of integrating several newcomers at once, on a weekly or bi-weekly basis, thereby reducing the frequency of stress-inducing introductions. To achieve this, incoming cats should be housed separately when first admitted, several individuals subsequently being moved into the established group simultaneously.”

To read more about cat colony housing and find recommendations from both The HSUS and shelters that have already created colony rooms, refer to the March-April issue of Animal Sheltering in the Back Issues section of our site.